I am currently looking into building a Speaker selector box for a friend, it is all line signal that will have two stereo outs and i need to do a summation to Mono. Am wondering weather to use relays with a low level current or just high quality Switches? also wondering what the best way to sum to Mono from a stereo signal? any help would be great.

The rotary switch has 4 pins in the middle (A, B, C & D) and 12 pins (1 to 12 anticlockwise) around the outside. It has 3 positions:
In the first, A connects to 1, B to 4, C to 7 and D to 10
In the 2nd, A connects to 2, B to 5, C to 8 and D to 11
You can work out the third!

SO, for each balanced stereo in and out there are four wires, yes? L+, L-, R+ and R-.